OBDII / Elm MPG meter. Almost working but not quite! - Page 7

esteban2 · 05-16-2005, 05:39 PM

Quote: Originally Posted by god_of_cpu

Post the log files for both the tester and your VB app. Also do you remember which line the assertion failures that your ignoring are happening on?

If your getting the same values over and over again, it probably means the main thread didn't start or stopped for some reason. Are you calling API_OBDII_Start before querying any packets? It could also mean there was an error reading the values from the ELM device. The logs should indicate this, but you can also catch this in your VB program by looking at the m_Flags member of the returned packet and seeing if it contains eOBDFlagError. You should never display a value if the packet flag indicates eOBDFlagError as it will be inaccurate.

You can also query values now with the CustomQuery call. This does not use the polling thread so it should ONLY be called before calling the Start function or after calling the stop function. It will block until it sends and recieves a response from the COM port, so you should not use this for displaying constantly updating values, but its easier to use for debugging purposes.

Code:

	//We can also get any packet data in single shot mode simply by calling API_OBDII_CustomQuery
	//Well query for the voltage of an oxygen senor by sending mode 1, PID 0x14
	if (g_Plugin.API_OBDII_CustomQuery(g_Plugin.m_lpUser, "01 14", &pktCustom))
	{
		//Now process the packet
		//Oxygen Sensor Voltage = .005 * A
		int iOxyVoltage = (int) (0.005 * pkt.m_Data[0]);
	}

I also recieved my new ELM v2.0 chip in and SetTimeout function now works, but there was a bug with it so I should post a new version soon that should allow up to double the refresh rate with the v2.0 chips.

Also post your VB source file and I'll talke a look at it.

Hi!!!!

I need your help please!!!!

I am writing code in Visual Basic in order to communicate to the ECU with ELM interface. I don’t know very well how to write and read the commands I have to send/receive to talk to the ECU.

Could you help me please?

I’ll appreciate your help!!!

Regards

Esteban

stevieg · 05-17-2005, 04:41 AM

Hello,

I hope this helps you:

http://www.mp3car.com/vbulletin/showthread.php?t=42802

I ended up using this, as it was simple use in Visual Basic.

rickster · 05-17-2005, 05:39 AM

Quote: Originally Posted by esteban2

Hi!!!!

I need your help please!!!!

I am writing code in Visual Basic in order to communicate to the ECU with ELM interface. I don’t know very well how to write and read the commands I have to send/receive to talk to the ECU.

Could you help me please?

I’ll appreciate your help!!!

Regards

Esteban

How many times have you got to post this same question in 3 different threads. I answered this the first time you posted, but you still insist on asking the same question.

planethax · 06-23-2007, 02:32 PM

I am missing something, I wanted to test this out but I do not have the faker.dll?

xbomb2 · 08-08-2007, 10:45 AM

Guys:

I am new here.
Basically I am interested to get MPG and ODOmeter reading from OBDII
connector. Can you guys tell me what is the code is the MPG and what is odometer reading.

If we have to get it indirectly what is the algorithm?

xbomb2 · 08-09-2007, 10:44 AM

I heard some car may send out MPG info via OBDII connector.
Can some of you genius tell me what are the strings?

god_of_cpu · 08-09-2007, 11:08 AM

The OBD II protocol does not support MPG and Odometer readings on any car. I know you can very unreliably guess at what the instantaneous MPG is based on some of the other sensors like mass air flow, but I'm not sure what calculation is.

Many cars use the OBDII port for things other then OBDII including manufacturer specific protocols that may support things like MPG and odometer readings, however, a generic OBDII adapter can not read these things no matter what software you use. You need a adapter and specific software to work with the adapter that has hacked the manufacturer specific protocol.

star-art · 09-01-2007, 09:41 PM

MPG can be calculated using speedometer and fuel used info. It is more reliable to use injector "on" timing than the amount of fuel remaining in the gas tank. That's because the tank float mechanism generates a varying signal for fuel level when the vehicle moves and fuel sloshes around inside the tank.

Ford EEC-IV and EEC-V computers have a fuel used signal that tells the trip computer how much gas has been burned. (Years ago, I spoke with a Ford service center about the wiring for the digital instrument cluster. They told me the fuel used input was pulled HIGH to 12V at up to 500 Hz. This signal corresponded to 48000 pulses per US gallon of fuel used. This jives with a patent filing I also found for measuring fuel used.)

If you don't have something like that, you might be able to get injector pulse width information from the PCM. If you know the rate of fuel flow in your injectors, you can calculate fuel used. Injectors are rated in pounds per hour. The injector is turned on for a number of milliseconds. The "on" time determines how much fuel flows through each injector. If I'm not mistaken, all injectors should have the same "on" time for a given throttle setting.

Once you know the fuel used, get mileage from your speedometer input. Nearly all cars have a speed sensor that generates so many pulses per mile travelled. Just count the pulses and divide per time (i.e. pulses per second). The MPG then equals the number of miles travelled divided by total fuel used.

Instantaneous economy is the MPG value updated each second. Average MPG is the instantaneous value averaged over a period of time. This time is the elapsed time since the Avg MPG value was last reset.

Hope that helps!

star-art · 09-01-2007, 09:44 PM

PS It would sure be nice if injectors were rated in "gallons per hour" or "liters per hour" instead of pounds. This means you need to estimate the volume of fuel flow by using the known density of gasoline to convert from mass to volume. I have no idea though if this density varies by grade of fuel. It might vary by temperature! So any conversion will yield only an estimate of the total fuel used.

1800eatMyDust · 09-23-2007, 02:04 PM

I'm interested in acquiring a wiring schematic for a 2005 Mustang GT with a V8 Engine. I'm particularly interested in knowing which pin on the ECU provides the signal for the Tachometer. I have installed a Digital Tach and cannot find the RPM signal to make it work.

Thanks

V/r

carcode · 09-29-2007, 02:08 PM

Simply read PID 0C out of the ECU with any OBD diagnostic tool. There you have the RPM.

sgwilliams · 06-23-2008, 11:06 AM

I would try Experts-Exchange.com, I'm an IT professional myself...almost promise you someone there can help...they haven't failed me yet. I use them for all kinds of different programming and hardware questions.

techbod · 06-24-2008, 11:53 AM

the VSS sensor would accomplish this many newer cars have this built in on display ( but only a guide ) to fuel consumption less the lead foot well you know what I mean

BiG K · 06-26-2008, 04:56 AM

I would say go for the injector on time. Also remember depending on the engine, the pressures vary, the higher the pressure the more fuel gets injected??

For example I have a 306 HDi & the injectors run at 1350bar....... (yup 1350 bar!!)

Guaging how much fuel left in the tank is VERY hit & miss. Fuel does slosh around ALOT!!

If and when you finish this and it works with my 306 HDi, I would be more than willing to pay you for it!

stavinski · 06-30-2008, 07:34 PM

So does this code in this thread work with ELM327, and is anyone willing to post their app they've already built?